1. Field of the Invention
This invention relates to ceramic products, for example, precision ceramic products such as bonding capillary, optical connector, wire guide, etc., and a process for producing the same.
2. Description of the Relevant Art
There have been used ceramic products, for example, as a carrier of gold wires for connecting electrodes with fingers of a lead frame on a semiconductor chip surface.
Such ceramic products are obtained generally by preparing a starting powder mixture comprising primarily alumina (Al.sub.2 O.sub.3) and additives such as chromia (Cr.sub.2 O.sub.3), magnesia (MgO), strontia (SrO), yttria (Y.sub.2 O.sub.5) or lantuna (La.sub.2 O.sub.3), etc., forming and sintering the powder mixture.
Processes for producing such ceramic products noted above are disclosed in Japanese Patent Application Laid-Open Print Nos. 97572/1984 (laid open June 5, 1984) and 291449/1986 (laid open Dec. 22, 1986), for example.
The process disclosed in the former Print No. 97572/1984 comprises the steps of mixing 0.01 to 5.0 mol% of chromia and 0.01 to 0.5 mol% of magnesia as additives into alumina, forming the mixture and then sintering the formed body in a vacuum below 10.sup.-1 torr at a temperature ranging from 1,400.degree. C. to 1,800.degree. C., to thereby facilitate control of the sintering atmosphere and reduce the amount of the additives.
The process disclosed in the latter Print No. 291449/1986 comprises the steps of mixing magnesium chloride or magnesium sulfate in aqueous solution into fine powder of alumina in the proportion of 0.1 to 3.0 mol% thereof, forming the mixture after drying and granulation, and then sintering the formed body in a vacuum of 10.sup.-3 torr at a temperature ranging from 1,400.degree. C. to 1,600.degree. C. (or 1,350.degree. C. to 1,550.degree. C. when the sintered body is further hot isostatically pressed), to thereby uniformly deposit spinel (MgAl.sub.2 O.sub.4) in the grain boundary layer of alumina whereby inhibiting abnormal growth of grains, so that pores remaining in the boundaries are reduced.
The products obtained by the process according to the former Print No. 97572/1984 have, however, a larger average grain size, resulting in inferior light transmissibility and hardness lower than 2000 HV, thus problems in machinability and mechanical durability would remain. On the other hand, in the process according to the latter Print No. 291449/1986, the sintering step should be performed in a vacuum, rendering the devices for performing the process large-scale. Further, in both of the Prints, there remain such drawbacks that the sintering steps are performed at high temperatures, respectively.